JPH0512749A - Method for detecting information from optical recording medium - Google Patents

Abstract

PURPOSE:To obtain two signals which are a playback signal based upon Kerr ellipticity and a playback signal based upon an angle of Kerr rotation at the same time from the same position on one medium when the optical recording medium is a medium which is variable individually in Kerr ellipticity and angle of Kerr rotation, namely, record and reproduce two bits (quad recording) at the same time at the same position of the medium, and to increase the density of the medium as a result. CONSTITUTION:When the information is detected from the optical recording medium 1 in this invention, linear polarized light is made incident on the optical recording medium 1 and its reflected light from the medium is spectrally diffracted by a half-mirror 13 into 1st split light and 2nd split light; and the 1st split light is detected by a specific 1st detection optical system to detect the playback signal based upon the Kerr ellipticity and also detected by a specific 2nd detection optical system to detect the playback signal based upon the angle of Kerr rotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes a linearly polarized laser spot incident on an optical recording medium to obtain a reproduction signal based on the Kerr ellipticity (η _K ) of the reflected light reflected by the medium, while the Kerr rotation of the reflected light is obtained. The present invention relates to a method for detecting information from an optical recording medium that enables a higher density of the optical recording medium by obtaining a reproduction signal based on the angle (θ _k ).

[0002]

BACKGROUND OF THE INVENTION Magneto-optical recording media and phase-change optical recording media have been actively researched and developed in recent years as large-capacity memories capable of rewriting recorded information, and have been practically used. Among them, in the magneto-optical recording medium, the Kerr effect that the polarization state of the reflected light changes depending on the direction of oxidation of the medium is generally used as the reproduction signal detecting means when the incident light is reflected by the medium. However, a method of converting the polarization state difference into light intensity using an optical element and thereby obtaining a reproduction signal is mainly adopted. On the other hand, the reproduction signal detecting means in the phase-change optical recording medium generally has the property that when the incident light is reflected by the medium, the reflectance is different because the optical constants in the medium are different between the crystalline state and the amorphous state. A method is mainly adopted in which the difference between the crystalline state and the amorphous state is converted into reflected light intensity by utilizing the above, and thereby a reproduced signal is obtained.

However, when detecting a reproduced signal in an optical recording medium in the related art, only one of the Kerr rotation angle-based detection method, the Kerr ellipticity-based detection method and the reflectance-based detection method is used. It has not been adopted and normally only one bit of information is associated with one position on the optical recording medium. Therefore, attempts have been made to perform multilevel recording by making the recording layers of the optical recording medium multi-layered (J
pn.J, Appl.Phys., Vol.28, p.343 (1989). However, there is a problem that the signal processing is complicated because the signal is detected only by the detection method based on the Kerr rotation angle.

Further, the following two methods have been proposed as methods for obtaining a reproduced signal by using the Kerr ellipticity. As one method, when circularly polarized light is made incident, a signal detection method using a so-called circular dichroic effect of a magnetic material, in which the intensity and phase of light differ depending on the direction of magnetization, is theoretically considered,
A method of detecting a differential signal at a bit boundary using a garnet film has been proposed (Journal of Japan Society of Applied Magnetics, Vol. 1).
2, 215-218, 1988). However, when a rare earth fiber metal alloy thin film is used as a recording medium, the circular dichroic effect is very small and it is difficult to practically use it as it is, and the S / N ratio of the obtained signal is not so high. It was not good.

Further, as another method, a method has been proposed in which the intensity of light reflected when circularly polarized light is incident differs depending on the direction of magnetization, and the magnetization information is directly detected as the intensity difference of reflected light. (Japanese Journal of Applied Magnetics, Vol.
13, 195-198, 1989). In such a case, the circular dichroic effect can be increased, but there is a problem that the S / N ratio of the obtained signal is not so good.

Therefore, conventionally, not only the magneto-optical recording medium but also the optical recording medium including the phase-change type optical recording medium has been densified by performing multi-valued recording, and the signal processing at that time can be simplified. In addition to this, a reproduction signal based on the Kerr ellipticity is added to the S
/ N There was a request to get better.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to obtain a reproduction signal based on the Kerr ellipticity with a good S / N ratio. An object of the present invention is to provide a method for detecting information from an optical recording medium, which can increase the density of an optical recording medium including a phase change type optical recording medium.

[0008]

SUMMARY OF THE INVENTION To achieve this object, a method of detecting information from an optical recording medium according to the present invention is a method of detecting information recorded on an optical recording medium from the optical recording medium,
Linearly polarized light is incident on the optical recording medium, and the reflected light reflected by this medium is split into first and second separated light by a half mirror, and the first separated light is azimuthally approximately 45 ° + 90 ° × n _1.
(Where n ₁ is an integer) is passed through a ¼ wavelength plate, and then is incident on a polarization beam splitter arranged at an azimuth of approximately 90 ° × n ₂ (where n ₂ is an integer) to obtain the P component. And the S component, and the P component and the S component are respectively detected by a photoelectric detector, the P component signal and the S component signal are differentially amplified, and a reproduction signal based on the Kerr ellipticity is detected. , The second separated light is incident on a polarization beam splitter arranged at an azimuth of approximately 45 ° + 90 ° × n ₃ (where n ₃ is an integer), and is divided into a P component and an S component. Of the P component and S
It is characterized in that a reproduced signal based on the Kerr rotation angle is detected by differentially amplifying the component signal.

The first separated light, which is a part of the reflected light, is passed through the azimuth 4
Pass through a quarter-wave plate of 5 ° + 90 ° × n ₁ (where n ₁ is an integer), then azimuth 90 ° × n ₂ (where n ₂ is an integer)
Since the polarization beam splitter is used to detect the P component and the S component separately, it is possible to obtain a reproduction signal by using the Kerr ellipticity η _K , as described later in “Detailed Description of the Invention”. it can. At this time, since the reproduction signal is detected by differentially amplifying the P component signal and the S component signal, in-phase noise can be removed and this reproduction signal can be obtained with a good S / N ratio. it can.

On the other hand, with the second separated light, a reproduction signal is obtained by differential detection based on the Kerr rotation angle. Therefore,
If the optical recording medium can change the Kerr ellipticity and the Kerr rotation angle separately, from the same position of one medium at the same time,
It is possible to obtain two signals, a reproduction signal based on the Kerr ellipticity and a reproduction signal based on the Kerr rotation angle. That is, two bits (four-value recording) are recorded at the same position on one medium at the same time.
The recording medium can be reproduced, and the density of the recording medium can be increased.

[0011]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, the optical recording medium according to the present embodiment is a medium in which the Kerr ellipticity and the Kerr rotation angle can be changed separately, and the details will be described later.

In the signal detecting method for the optical recording medium according to the present embodiment, as shown in FIG. 1, for example, the linearly polarized laser light emitted from the laser 11 which is a semiconductor laser is
The light enters the non-polarizing beam splitter 12, and a part of the light is reflected and then passes through the non-polarizing beam splitter 12 to be condensed on the optical recording medium 1 by a focusing lens (not shown). The half mirror 13 splits the reflected light reflected by the medium 1 into first and second separated lights.

In the present embodiment, the first separated light is guided to the first detection optical system 20 to obtain a reproduction signal based on the Kerr ellipticity, while the second separated light is guided to the second detection optical system 30 to rotate the Kerr. You are getting a playback signal based on the corners.

That is, in the first detection optical system 20,
The first separated light is transmitted from the half mirror 13 to the quarter wavelength plate (λ
/ 4 plate) 23. The quarter wave plate 23 has an azimuth θ of 40 ° + 90 ° × n ₁ ≦ θ ≦ 50 ° + 90 °
× a n _1, is arranged substantially 45 ° + 90 ° × n ₁ orientation, is the phase delay δ, λ / 4-0.05λ ≦ δ
It is set to ≦ λ / 4 + 0.05λ. The first separated light is changed from linearly polarized light to circularly polarized light by passing through such a quarter wave plate 23.

The circularly polarized light is then guided to the polarization beam splitter 24. The polarization beam splitter 24 has an azimuth θ of −5 ° + 90 ° × n.
₂ ≦ θ ≦ 5 ° + 90 ° × n ₂ and they are arranged in almost 90 ° × n ₂ azimuth. The light converted into circularly polarized light by the polarization beam splitter 24 arranged in this way is converted into P
It is divided into a component and an S component.

The P component and the S component are detected by the photoelectric detectors 25a and 25b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 26, resulting in the Kerr ellipticity. A reproduced signal based on the detected signal is detected.

On the other hand, in the second detection optical system 30, the second separated light is guided from the half mirror 13 to the polarization beam splitter 34. This polarization beam splitter 34
Are arranged at an azimuth of approximately 45 ° + 90 ° × n ₃ .
The second separated light is divided into a P component and an S component by the polarization beam splitter 34 arranged in this way.

The P component and the S component are detected by the photoelectric detectors 35a and 35b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 36, resulting in the Kerr rotation angle. A reproduced signal based on the detected signal is detected.

As described above, the optical recording medium is a medium in which the Kerr ellipticity and the Kerr rotation angle can be changed separately, and the reproduction signal based on the Kerr ellipticity and the Kerr rotation can be obtained from the same position of one optical recording medium. Two signals, a corner-based playback signal, can be obtained simultaneously. That is, 2-bit (four-valued recording) recording / reproducing can be performed at the same position on one medium at the same time, and the density of the recording medium can be increased. Further, since the signal based on the Kerr ellipticity and the signal based on the Kerr rotation angle are differentially detected, a reproduced signal can be obtained with a good S / N ratio.

As described above, in order to obtain the two signals based on the Kerr ellipticity and the Kerr rotation angle, the medium may be any one as long as the optical recording medium can change the Kerr ellipticity and the Kerr rotation angle separately. For example, the following can be exemplified.

As an example, the recording film of the optical recording medium has a two-layer structure of a magneto-optical recording film (MO film) and a phase change film,
The change in the optical constant of the phase change film and the interference structure are used. The magnetization direction of the magneto-optical recording film changes vertically, while the optical constants of the phase change recording film change to N ₁ and N ₂ depending on whether it is crystalline or amorphous. By the combination of the direction of magnetization and the optical constant,
The magnetic Kerr effect of an optical recording medium can be classified as follows.

Utilizing the interference structure, η _k2 ≠ η _k1 , θ _k1 ≈
If the medium is designed so as to be θ _k2 , the direction of θ _k is different depending on the upper and lower sides of the magnetization, and further, it corresponds to the optical constant.
The magnitude of η _k is different. Therefore, it is possible to detect the upper and lower sides of the magnetization and the difference in the optical constants separately.

[0023]

[Table 1]

As another example, a recording film of an optical recording medium is
A two-layer structure of two magneto-optical recording films (MO films) is used. One of the magneto-optical recording films has a large Kerr rotation angle and the Kerr ellipticity is small, and the other magneto-optical recording film has the opposite design. To do. Also in this case, the signal based on the Kerr rotation angle and the signal based on the Kerr ellipticity can be simultaneously recorded / reproduced.

The optical recording medium to which the signal detecting method according to the present invention is applied is not limited to the above-mentioned example, and it is only necessary that the optical recording medium can change the Kerr ellipticity and the Kerr rotation angle separately. Of course.

Next, by the constitution of the first detection optical system 20,
The principle by which the reproduction signal can be obtained using the Kerr ellipticity η will be described. Linearly polarized light is made incident on the optical recording medium, and the azimuth of the polarization direction at this time is set to 0 °. The reflected light including the reproduction information reflected by the optical recording medium 1 is approximately

[0027]

[Equation 1]

Is represented by The quarter-wave plate 23 arranged in the azimuth at about 45 ° (η ₁ = 0)

[0029]

[Equation 2]

It is expressed as follows. The polarization beam splitter 24 arranged in the 0 ° (η ₃ = 0) direction has a P component and an S component, respectively.

[0031]

[Equation 3]

It is expressed as follows. Therefore, the reflected light reflected by the optical recording medium 1 passes through the quarter wavelength plate 23, and the electric field vectors E ₁ and E ₂ of the P component and the S component, which are separated by the polarization beam splitter 24, are respectively

[0033]

[Equation 4]

It is expressed as follows. Therefore, the intensity I of the P component
₁ , the intensity I _{2 of the} S component is

[0035]

[Equation 5]

It is expressed as follows. In this embodiment, since differential detection is performed, the differential signal S is expressed as S = I ₂ −I ₁ = 2θ _K. Since this S equation is expressed only by η which is the Kerr ellipticity, it has been proved that the optical detection system configured as shown in FIG.

In this way, the reflected light reflected by the optical recording medium 1 is converted into a quarter wave plate 23 having an azimuth of 45 ° + 90 ° × n _1.
, And then the polarization beam splitter 24 having an azimuth of 90 ° × n ₂ is used to detect the P component and the S component separately. Therefore, as described above, the reproduction signal is obtained using the Kerr ellipticity η _K. Obtainable.

Of course, the present invention is not limited to the above embodiment. In particular, an optical recording medium to which the signal detection method according to the present invention can be applied is, as described above, an optical recording medium including a magneto-optical recording film and a phase change film, and a magneto-optical recording medium including two magneto-optical recording films. It may be either. Further, although the magneto-optical recording film and the phase change film are exemplified below, it is needless to say that the magneto-optical recording film and the phase change film may be various ones.

Magneto-Optical Recording Film The magneto-optical recording film is (i) at least one selected from 3d transition genus and (iii) at least one selected from rare earths.
Or at least one selected from the group consisting of 3d transition metals, and (ii) a corrosion-resistant metal.
(Iii) It is preferably composed of at least one element selected from rare earths.

(I) 3d transition metals include Fe and C
O, Ti, V, Cr, Mn, Ni, Cu, Zn or the like is used, and Fe or Co or both of them is preferable.

This 3d transition metal is contained in the magneto-optical recording film in an amount of 2
It is present in an amount of 0 to 90 atom%, preferably 30 to 85 atom%, more preferably 35 to 80 atom%. (Ii) The corrosion resistance of the magneto-optical recording film can be enhanced by including the corrosion-resistant metal in the magneto-optical recording film. Such corrosion resistant metals include Pt, Pd,
Ti, Zr, Ta, Nb, etc. are used, and among these, Pt, Pd, and Ti are preferable, and Pt, Pd, or both are particularly preferable.

This corrosion resistant metal is contained in the magneto-optical recording film in an amount of 3
It is present in an amount of 0 atomic% or less, preferably 5 to 25 atomic%, more preferably 10 to 25 atomic%, and further preferably 10 to 20 atomic%.

Examples of the rare earth element (iii) include the following elements. Gd, Tb, Dy, Ho, Er,
Tm, Yb, Lu, La, Ce, Pr, Nd, Pm, S
m, Eu Of these, Gd, Tb, Dy, Ho, Nd, Sm, and Pr are preferably used.

At least one selected from the above group
The rare earth element as a seed is present in the magneto-optical recording film in an amount of 5 to 50 atom%, preferably 8 to 45 atom%, and more preferably 10 to 40 atom%.

In the present invention, a small amount of various elements may be added to the magneto-optical recording film to improve the Curie temperature, the compensation temperature, the coercive force Hc, the Kerr rotation angle θk, or reduce the cost. These elements can be used in a ratio of, for example, less than 10 atom% with respect to the total number of atoms constituting the recording film.

Examples of other elements that can be used in combination include the following elements. (I) 3d transition element other than Fe and Co Specifically, Sc, Ti, V, Cr, Mn, Ni, C
u and Zn are used.

Of these, Ti, Ni, Cu, Zn and the like are preferably used. (II) 4d transition element other than Pd Specifically, Y, Zr, Nb, Mo, Tc, Ru, R
h, Ag and Cd are used.

Of these, Zr and Nb are preferably used. (III) 5d transition element other than Pt Specifically, Hf, Ta, W, Re, Os, Ir, A
u and Hg are used.

Of these, Ta is preferably used. (IV) Group IIIB element Specifically, B, Al, Ga, In and Tl are used.

Of these, B, Al and Ga are preferably used. (V) Group IVB element Specifically, C, Si, Ge, Sn, and Pb are used.

Of these, Si, Ge, Sn and Pb are preferably used. (VI) Group VB element Specifically, N, P, As, Sb and Bi are used.

Of these, Sb is preferably used. (VII) VIB Group Element Specifically, S, Se, Te and Po are used.

Of these, Te is preferably used. The magneto-optical recording film having the above composition has an easy axis of magnetization perpendicular to the film surface, and is often an amorphous thin film capable of perpendicular magnetic and magneto-optical recording showing a square loop with good Kerr hysteresis. That is confirmed by wide-angle X-ray diffraction.

In the present specification, the expression of a square loop having good Kerr hysteresis means that the Kerr rotation angle (θk ₁ ) which is the Kerr rotation angle in the maximum external magnetic field and the Kerr rotation angle when the external magnetic field is zero remain. Car rotation angle (θk
₂ ) and the ratio θk ₂ / θk ₁ is 0.8 or more.

The film thickness of this magneto-optical recording film is 100 to 600.
Å, preferably 100-400 Å, more preferably 20
It is about 0 to 350Å. Particularly, magneto-optical recording films suitable for the Kerr ellipticity include TbFe, TbCo and Tb.
FeCo, GdFe, GdCo, GdFeCo, GdT
bFe, GdTbCo, GdTbFeCo, NdFe,
NdCo, NdTbFe, NdTbCo, NdTbFe
Co, DyFe, DyCo, DyTbFe, DyTbC
A magneto-optical recording film made of o, DyTbFeCo, CoPt, CoPd is preferable.

Phase Change Film Any phase change film may be used as long as its optical constant changes in accordance with a change in state, and TeO, TeFeO, TeFe.
Su, TeGeOSu, TeGe, TeGeSe, Te
GeSb, TeGeSeSb, InSe, InSeTl
Co, SbTe, SnTeSe, GaSeTe, GaS
A recording film such as eTe, GaSeTeGe, BiTeSbSe can be used.

[0057]

As described above, in the present invention, the first separated light, which is a part of the reflected light, has an azimuth of 45 ° + 90 ° × n ₁
Of ¼ wave plate, then azimuth 90 ° × n ₂
Since the polarization beam splitter is used to detect the P component and the S component separately, a reproduction signal can be obtained by using the Kerr ellipticity η _K. At this time, since the reproduced signal is detected by differentially amplifying the P component signal and the S component signal, this reproduced signal can be obtained with a good S / N ratio.

On the other hand, in the second separated light, a reproduction signal is obtained by differential detection based on the Kerr rotation angle. Therefore,
If the optical recording medium can change the Kerr ellipticity and the Kerr rotation angle separately, from the same position of one medium at the same time,
It is possible to obtain two signals, a reproduction signal based on the Kerr ellipticity and a reproduction signal based on the Kerr rotation angle. That is, two bits (four-value recording) are recorded at the same position on one medium at the same time.
The recording medium can be reproduced, and the density of the recording medium can be increased.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system used in a signal detection method for an optical recording medium according to an embodiment of the present invention.

[Explanation of symbols]

 1 Optical Recording Medium 13 Half Mirror 24 Quarter Wave Plate 25 Polarizing Beam Splitter 25a, 25b Photoelectric Detector 34 Polarizing Beam Splitter 35a, 35b Photoelectric Detector

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 1, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Method for detecting information from optical recording medium

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes a linearly polarized laser spot incident on an optical recording medium to obtain a reproduction signal based on the Kerr ellipticity (η _K ) of the reflected light reflected by the medium, while the Kerr rotation of the reflected light is obtained. The present invention relates to a method for detecting information from an optical recording medium that enables a higher density of the optical recording medium by obtaining a reproduction signal based on the angle (θ _k ).

[0002]

BACKGROUND OF THE INVENTION Magneto-optical recording media and phase-change optical recording media have been actively researched and developed in recent years as large-capacity memories capable of rewriting recorded information, and have been practically used. Among them, in the magneto-optical recording medium, the Kerr effect that the polarization state of the reflected light changes depending on the direction of oxidation of the medium is generally used as the reproduction signal detecting means when the incident light is reflected by the medium. However, a method of converting the polarization state difference into light intensity using an optical element and thereby obtaining a reproduction signal is mainly adopted. On the other hand, the reproduction signal detecting means in the phase-change optical recording medium generally has the property that when the incident light is reflected by the medium, the reflectance is different because the optical constants in the medium are different between the crystalline state and the amorphous state. A method is mainly adopted in which the difference between the crystalline state and the amorphous state is converted into reflected light intensity by utilizing the above, and thereby a reproduced signal is obtained.

However, when detecting a reproduced signal in an optical recording medium in the related art, only one of the Kerr rotation angle-based detection method, the Kerr ellipticity-based detection method and the reflectance-based detection method is used. It has not been adopted and normally only one bit of information is associated with one position on the optical recording medium. Therefore, attempts have been made to perform multilevel recording by making the recording layers of the optical recording medium multi-layered (J
pn.J, Appl.Phys., Vol.28, p.343 (1989). However, there is a problem that the signal processing is complicated because the signal is detected only by the detection method based on the Kerr rotation angle.

Further, the following two methods have been proposed as methods for obtaining a reproduced signal by using the Kerr ellipticity. As one method, when circularly polarized light is made incident, a signal detection method using a so-called circular dichroic effect of a magnetic material, in which the intensity and phase of light differ depending on the direction of magnetization, is theoretically considered,
A method of detecting a differential signal at a bit boundary using a garnet film has been proposed (Journal of Japan Society of Applied Magnetics, Vol. 1).
2, 215-218, 1988). However, when a rare earth- transition metal alloy thin film is used as a recording medium, the circular dichroic effect is very small and it is difficult to practically use it as it is, and the S / N ratio of the obtained signal is not so high. It was not good.

Further, as another method, a method has been proposed in which the intensity of light reflected when circularly polarized light is incident differs depending on the direction of magnetization, and the magnetization information is directly detected as the intensity difference of reflected light. (Japanese Journal of Applied Magnetics, Vol.
13, 195-198, 1989). In such a case, the circular dichroic effect can be increased, but there is a problem that the S / N ratio of the obtained signal is not so good.

Therefore, conventionally, not only the magneto-optical recording medium but also the optical recording medium including the phase-change type optical recording medium has been densified by performing multi-valued recording, and the signal processing at that time can be simplified. In addition to this, a reproduction signal based on the Kerr ellipticity is added to the S
There was a request to obtain a good / N ratio .

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is possible to obtain a reproduction signal based on the Kerr ellipticity with a good S / N ratio. An object of the present invention is to provide a method for detecting information from an optical recording medium, which can increase the density of an optical recording medium including a phase change type optical recording medium.

[0008]

SUMMARY OF THE INVENTION To achieve this object, a method of detecting information from an optical recording medium according to the present invention is a method of detecting information recorded on an optical recording medium from the optical recording medium,
Linearly polarized light is incident on the optical recording medium, and the reflected light reflected by this medium is split into first and second separated light by a half mirror, and the first separated light is azimuthally approximately 45 ° + 90 ° × n _1.
(Where n ₁ is an integer) is passed through a ¼ wavelength plate, and then is incident on a polarization beam splitter arranged at an azimuth of approximately 90 ° × n ₂ (where n ₂ is an integer) to obtain the P component. And the S component, and the P component and the S component are respectively detected by a photoelectric detector, the P component signal and the S component signal are differentially amplified, and a reproduction signal based on the Kerr ellipticity is detected. , The second separated light is incident on a polarization beam splitter arranged at an azimuth of approximately 45 ° + 90 ° × n ₃ (where n ₃ is an integer), and is divided into a P component and an S component. Of the P component and S
It is characterized in that a reproduced signal based on the Kerr rotation angle is detected by differentially amplifying the component signal.

The first separated light, which is a part of the reflected light, is passed through the azimuth 4
Pass through a quarter-wave plate of 5 ° + 90 ° × n ₁ (where n ₁ is an integer), then azimuth 90 ° × n ₂ (where n ₂ is an integer)
Since the polarization beam splitter is used to detect the P component and the S component separately, it is possible to obtain a reproduction signal by using the Kerr ellipticity η _K , as described later in “Detailed Description of the Invention”. it can. At this time, since the reproduction signal is detected by differentially amplifying the P component signal and the S component signal, in-phase noise can be removed and this reproduction signal can be obtained with a good S / N ratio. it can.

On the other hand, with the second separated light, a reproduction signal is obtained by differential detection based on the Kerr rotation angle. Therefore,
If the optical recording medium can change the Kerr ellipticity and the Kerr rotation angle separately, from the same position of one medium at the same time,
It is possible to obtain two signals, a reproduction signal based on the Kerr ellipticity and a reproduction signal based on the Kerr rotation angle. That is, two bits (four-value recording) are recorded at the same position on one medium at the same time.
The recording medium can be reproduced, and the density of the recording medium can be increased.

[0011]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, the optical recording medium according to the present embodiment is a medium in which the Kerr ellipticity and the Kerr rotation angle can be changed separately, and the details will be described later.

In the signal detecting method for the optical recording medium according to the present embodiment, as shown in FIG. 1, for example, the linearly polarized laser light emitted from the laser 11 which is a semiconductor laser is
The beam is incident on the beam splitter 12, part of which is reflected, then passes through the beam splitter 12, and is focused on the optical recording medium 1 by a focusing lens (not shown). The half mirror 13 reflects the reflected light reflected by the medium 1.
Is split into the first and second separated lights.

In the present embodiment, the first separated light is guided to the first detection optical system 20 to obtain a reproduction signal based on the Kerr ellipticity, while the second separated light is guided to the second detection optical system 30 to rotate the Kerr. You are getting a playback signal based on the corners.

That is, in the first detection optical system 20,
The first separated light is transmitted from the half mirror 13 to the quarter wavelength plate (λ
/ 4 plate) 23. The quarter wave plate 23 has an azimuth θ of 40 ° + 90 ° × n ₁ ≦ θ ≦ 50 ° + 90 °
× a n _1, is arranged substantially 45 ° + 90 ° × n ₁ orientation, is the phase delay δ, λ / 4-0.05λ ≦ δ
It is set to ≦ λ / 4 + 0.05λ. The first separated light is changed from linearly polarized light to circularly polarized light by passing through such a quarter wave plate 23.

The circularly polarized light is then guided to the polarization beam splitter 24. The polarization beam splitter 24 has an azimuth θ of −5 ° + 90 ° × n.
₂ ≦ θ ≦ 5 ° + 90 ° × n ₂ and they are arranged in almost 90 ° × n ₂ azimuth. The light converted into circularly polarized light by the polarization beam splitter 24 arranged in this way is converted into P
It is divided into a component and an S component.

The P component and the S component are detected by the photoelectric detectors 25a and 25b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 26, resulting in the Kerr ellipticity. A reproduced signal based on the detected signal is detected. Furthermore
Between the λ / 4 plate 23 and the polarization beam splitter 24
By inserting a λ / 2 plate into it and determining the azimuth angle appropriately.
The P component and S component generated in optical elements and magneto-optical recording media
The phase difference with the minute can be canceled and the S / N ratio of the reproduced signal can be adjusted.
It is also possible to improve further.

On the other hand, in the second detection optical system 30, the second separated light is guided from the half mirror 13 to the polarization beam splitter 34. This polarization beam splitter 34
Are arranged at an azimuth of approximately 45 ° + 90 ° × n ₃ .
The second separated light is divided into a P component and an S component by the polarization beam splitter 34 arranged in this way.

The P component and the S component are detected by the photoelectric detectors 35a and 35b, respectively, and the P component signal and the S component signal are differentially amplified by the differential amplifier 36, resulting in the Kerr rotation angle. A reproduced signal based on the detected signal is detected. Also
Half mirror 13 and polarized beam sp
Insert λ / 2 plate with azimuth angle π / 8 between liter 34
It is also possible to do so.

As described above, the optical recording medium is a medium in which the Kerr ellipticity and the Kerr rotation angle can be changed separately, and the reproduction signal based on the Kerr ellipticity and the Kerr rotation can be obtained from the same position of one optical recording medium. Two signals, a corner-based playback signal, can be obtained simultaneously. That is, 2-bit (four-valued recording) recording / reproducing can be performed at the same position on one medium at the same time, and the density of the recording medium can be increased. Further, since the signal based on the Kerr ellipticity and the signal based on the Kerr rotation angle are differentially detected, a reproduced signal can be obtained with a good S / N ratio.

As described above, in order to obtain the two signals based on the Kerr ellipticity and the Kerr rotation angle, the medium may be any one as long as the optical recording medium can change the Kerr ellipticity and the Kerr rotation angle separately. For example, the following can be exemplified.

As an example, the recording film of the optical recording medium has a two-layer structure of a magneto-optical recording film (MO film) and a phase change film,
The change in the optical constant of the phase change film and the interference structure are used. The magnetization direction of the magneto-optical recording film changes vertically, while the optical constants of the phase change recording film change to N ₁ and N ₂ depending on whether it is crystalline or amorphous. By the combination of the direction of magnetization and the optical constant,
The magnetic Kerr effect of an optical recording medium can be classified as follows.

Utilizing the interference structure, η _k2 ≠ η _k1 , θ _k1 ≈
If the medium is designed so as to be θ _k2 , the direction of θ _k is different depending on the upper and lower sides of the magnetization, and further, it corresponds to the optical constant.
The magnitude of η _k is different. Therefore, it is possible to detect the upper and lower sides of the magnetization and the difference in the optical constants separately.

[0023]

[Table 1]

Kerr ellipticity (η _k ) and Kerr rotation angle
(Θ _k ) is the substrate, magneto-optical recording film, phase change film and
And optical constants of the enhanced film (refractive index n and extinction coefficient k)
And calculated from the media configuration, etc. Therefore,
By selecting and setting these parameters appropriately
Therefore, the design of the medium such that η _k2 ≠ η _k1 , θ _k1 ≈ θ _k2
It is possible.

Consider, for example, the following optical recording medium.
It

[0026]

[Table 2]

The disk structure is the substrate / SiN film (100
0Å) / magneto-optical recording film (65Å) / SiN film (280
Å) / Laser light used as a phase change film (1000 Å)
Is 830 nm, θ _k and η _k are
Desired.

[0028]

[Table 3]

As another example, a recording film of an optical recording medium is
A two-layer structure of two magneto-optical recording films (MO films) is used. One of the magneto-optical recording films has a large Kerr rotation angle and the Kerr ellipticity is small, and the other magneto-optical recording film has the opposite design. To do. Also in this case, the signal based on the Kerr rotation angle and the signal based on the Kerr ellipticity can be simultaneously recorded / reproduced.

The optical recording medium to which the signal detecting method according to the present invention is applied is not limited to the above-mentioned example, and may be any medium that can change the Kerr ellipticity and the Kerr rotation angle separately. Of course.

Next, with the configuration of the first detection optical system 20,
The principle by which the reproduction signal can be obtained using the Kerr ellipticity η will be described. Direction of polarization of linearly polarized light incident on an optical recording medium
The direction is defined as an azimuth of 0 °.

Jones vector of the electric field vector of the incident light
Le

[0033]

[Equation 1]

Then, the reproduction information reflected by the optical recording medium is
The Jones vector of the reflected light including the information is approximately

[0035]

[Equation 2 ]

It is expressed as follows. The Jones matrix of the quarter-wave plate 23 oriented at about 45 ° (n ₁ = 0).
Cous

[0037]

[Equation 3 ]

Is represented by 0 ° (n ₃ = 0) Jones Ma of the polarizing beam splitter 24 arranged in a direction
The tricks are for P component and S component respectively.

[0039]

[Equation 4]

It is represented by Therefore, the reflected light reflected by the optical recording medium 1 passes through the quarter wavelength plate 23, and the electric field vectors E ₁ and E ₂ of the P component and the S component, which are separated by the polarization beam splitter 24, are respectively

[0041]

[Equation 5]

It is expressed as follows. Therefore, the intensity I of the P component
₁ , the intensity I _{2 of the} S component is

[0043]

[Equation 6]

It is expressed as follows. In this embodiment, since differential detection is performed, the differential signal S is expressed as S = I ₂ −I ₁ = 2 η _k . This differential signal S has a Kerr ellipticity η _k
It is proved that the reproduction signal is obtained by using the Kerr ellipticity by the optical detection system configured as shown in FIG.

As described above, the reflected light reflected by the optical recording medium 1 is converted into a quarter wave plate 23 having an azimuth of 45 ° + 90 ° × n _1.
, And then the polarization beam splitter 24 having an azimuth of 90 ° × n ₂ is used to detect the P component and the S component separately. Therefore, as described above, the reproduction signal is obtained using the Kerr ellipticity η _K. Obtainable.

Of course, the present invention is not limited to the above embodiment. In particular, an optical recording medium to which the signal detection method according to the present invention can be applied is, as described above, an optical recording medium including a magneto-optical recording film and a phase change film, and a magneto-optical recording medium including two magneto-optical recording films. It may be either. Further, although the magneto-optical recording film and the phase change film are exemplified below, it is needless to say that the magneto-optical recording film and the phase change film may be various ones.

Magneto-Optical Recording Film The magneto-optical recording film used in the present invention is particularly
Although not limited, for example, at least one selected from (A) (i) 3d transition metals
Element and at least one selected from (iii) rare earths
An alloy consisting of an element of (B) (i) at least one selected from 3d transition metals
Elements, (ii) corrosion-resistant metals, and (iii) rare earths
Alloy consisting of at least one element selected from (C) (i) at least one selected from 3d transition metals
Examples of the alloy include the alloy of (1 ) and (ii) a corrosion-resistant metal, (D) Pt / Co composition modulation film, or (E) Pd / Co composition modulation film.

Examples of the 3d transition metal include Fe and C
o, Ti, V, Cr, Mn, Ni, Zn, etc. are used.
It In the alloy films of (A) and (B) above, 3d
The content of transition metal is 20 to 90 atomic%, preferably 3
It is desirable that the content of (C) is 0 to 85 atom%.
In the gold film, the content of 3d transition metal is 10 to 60 original
It is desirable to be child%.

As the rare earth element, for example, Gd,
Tb, Dy, Ho, Er, Tm, Nd, Sm, Pr, etc.
Used. Odors in the alloy films of (A) and (B) above
The content of the rare earth element is 5 to 50 atomic%, preferably
Is preferably 8 to 45 atomic%.

Examples of corrosion-resistant metals include Pt and P
d, Ti, Zr, Ta, Nd, etc. are used. the above
In the alloy film of (B), the content of corrosion resistant metal is 3
0 atomic% or less, preferably 5 to 25 atomic%
desirable. In addition, in the alloy film of (C) above, corrosion resistance
The content of the functional metal is preferably 90 to 40 atomic%.
Yes.

In particular, a magneto-optical recording suitable for the case of Kerr ellipticity
As the recording film, TbFe, TbFeCo, GdFe, G
dFeCo, GdTbFe, GdTbFeCo, NdT
bFe, NbTbFeCo, CoPt, CoPt, Co
Pd, DyTbFe, DyTbFeCo, TbCo, G
It consists of dCo, GdTbCo, DyTbCo, NdFe
A magneto-optical recording film is preferable.

The thickness of this magneto-optical recording film is preferably 50.
~ 600 angstroms, more preferably 50-40
0 angstrom, more preferably 50-350 on
It is about Gstrom.

Phase Change Film Any phase change film may be used as long as its optical constant changes in response to a change in state, and TeO, TeFeO, TeFe.
S n, TeGeOS n, TeGe, TeGeSe, Te
GeSb, TeGeSeSb, InSe, InSeTl
Co, SbTe, SnTeSe, GaSeTe, GaS
A recording film such as eTe, GaSeTeGe, BiTeSbSe can be used.

[0054]

As described above, in the present invention, the first separated light, which is a part of the reflected light, has an azimuth of 45 ° + 90 ° × n ₁
Of ¼ wave plate, then azimuth 90 ° × n ₂
Since the polarization beam splitter is used to detect the P component and the S component separately, a reproduction signal can be obtained by using the Kerr ellipticity η _K. At this time, since the reproduced signal is detected by differentially amplifying the P component signal and the S component signal, this reproduced signal can be obtained with a good S / N ratio.

On the other hand, in the second separated light, a reproduction signal is obtained by differential detection based on the Kerr rotation angle. Therefore,
If the optical recording medium can change the Kerr ellipticity and the Kerr rotation angle separately, from the same position of one medium at the same time,
It is possible to obtain two signals, a reproduction signal based on the Kerr ellipticity and a reproduction signal based on the Kerr rotation angle. That is, two bits (four-value recording) are recorded at the same position on one medium at the same time.
The recording medium can be reproduced, and the density of the recording medium can be increased.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system used in a signal detection method for an optical recording medium according to an embodiment of the present invention.

[Explanation of Codes] 1 Optical recording medium 13 Half mirror 24 Quarter wave plate 25 Polarizing beam splitter 25a, 25b Photoelectric detector 34 Polarizing beam splitter 35a, 35b Photoelectric detector ───────────── ──────────────────────────────────────────

[Procedure amendment]

[Submission date] October 5, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction content]

Phase Change Film Any phase change film may be used as long as its optical constant changes in response to a change in state, and TeO, TeFeO, TeFe.
Sn, TeGeOSn, TeGe, TeGeSe, Te
GeSb, TeGeSeSb, InSe, InSeTl
Co, SbTe, SnTeSe, GaSeTe, GaS
A recording film such as eTe, GaSeTeGe, BiTeSbSe can be used. The thickness of this phase change film is preferably
50 to 2000 angstroms, more preferably
Is 50 to 1000 angstroms.

Claims (1)

Claim: What is claimed is: 1. A method for detecting information recorded on an optical recording medium from an optical recording medium, the method comprising: incident linearly polarized light on the optical recording medium and reflecting the reflected light on the medium. Is split into a first and a second separated light by a half mirror, and the first separated light is passed through a quarter-wave plate arranged at an azimuth of approximately 45 ° + 90 ° × n ₁ (n ₁ is an integer), and then , Is incident on a polarizing beam splitter arranged at an azimuth of approximately 90 ° × n ₂ (n ₂ is an integer), and is divided into a P component and an S component, and these P component and S component are detected by a photoelectric detector, The P-component signal and the S-component signal are differentially amplified to detect the reproduction signal based on the Kerr ellipticity, while the second separated light is emitted at an azimuth of approximately 45 ° + 90 ° × n ₃ (n ₃ is an integer). It is made incident on the polarization beam splitter arranged at, and is divided into P component and S component, An optical recording characterized by detecting the P component and the S component respectively by a photoelectric detector, differentially amplifying the P component signal and the S component signal, and detecting a reproduction signal based on the Kerr rotation angle. A method of detecting information from a medium.